Photoconductive materials have been widely exploited as the basis for various imaging processes. Several of these processes have employed a photoconductor as an electrode for controlling (with light) an electrochemical reaction. R. L. Carlson (Photographic Science and Engineering, Vol. 8, p. 167, (1964)), and E. G. Johnson and B. W. Neher (U.S. Pat. No. 3,010,883 (1950)) describe electrolytic photography processes in which a ZnO photoconductive (dark-insulating) cathode is used to reduce a metal salt (Ni.sup.+2, Cu.sup.+2, Ag.sup.+) to the corresponding metal. Other photoconductors which have been employed in these and related applications include CdS and PbS, (R. E. Stralle, U.S. Pat. No. 3,623,287 (1971)) and Ge (G. Karadzhov and M. Igor, Izv. Otd. Khim Navki, Bulg. Akad. Nauk., Vol. 7, 331-338 (1974)). While the details of such processes vary in many respects, all produce images which are two-dimensional projections of the original image. Carlson reported depositing Ni in sufficient density to create an optically reflective image.
In only a few instances was the resolution of these photographic processes actually reported. However, the majority of examples involved relatively thick layers of granular, polycrystalline photoconductors (ZnO or CdS) which would not be capable of providing exceptionally good resolution. R. D. Weiss, (Photographic Science and Egineering, Vol. 11, 287-292 (1967)) reported resolution of 7-9 line pairs/mm (1 pm) for electrolytic conversion of a leuco dye using a photoconductive anode of this sort. Stralle described a device for making holographic recordings using a very thin (0.1 to 0.5 micrometer) film of CdS or PbS as a photoanode. Under the influence of light, these materials dissolved electrochemically, leaving a positive photographic image in the form of a pattern of holes etched in the photoconductive film. Line spacings as small as 1.5 micrometers (equivalent to 667 lpm) could be resolved with this technique.
Mazur (U.S. Pat. No. 4,512,855 (1985)), described an electrochemical process for creating metal interlayers within organic polymer films. This process relies upon the ability of certain electrochemically active polymer films to accept electrons from one surface of the polymer film while, simultaneously, metal ions diffuse into the polymer film from a solution at an opposed surface. When the transport properties for ions and electrons are suitable, and the redox potential for the polymer is negative with respect to that of the metal, a steady-state current density, I, can be established which corresponds to the electrodeposition of metal within the polymer film at a constant rate to form a discrete interlayer at a fixed distance, d, from the polymer/cathode interface. The magnitude of this current is related to the thickness of the film t, the transport parameters, the concentration of metal ions ([M.sup.n+ ] in solution, and the magnitude of the potential E at the polymer/cathode interface. The transverse location of deposition, d, is also determined by the same set of parameters. Therefore, both I and d may be controlled by appropriate selection of the process variables, particularly E and [M.sup.n+ ]. These phenomena were demonstrated by examples involving a polyimide film with the metals Ag and Cu.
Metal interlayers can be grown imagewise, as described by Mazur, by restricting the supply of either electrons or ions to specified regions of the polymer surfaces. This phenomenon was demonstrated, for example, by the use of a patterned cathode on the one hand and a patterned ion-barrier mask on the other. Both of these methods effectively function as on/off switches, i.e., the current density may be only one of two values: zero or a normal value. Consequently the patterns so generated can vary in two dimensions in a plane parallel to the polymer surface. Also, multiple interlayers may be grown by altering one or more of the process variables. However, if two or more interlayers are to be deposited, each with an independent pattern which varies in two dimensions, then the cathode or ion-barrier mask would have to be changed.